Increasing the bandwidth of data transfer on transmission conduits is extremely important in today's high volume information transmission environment. The need for broader telecommunication bandwidths comes from several modern data transmission requirements. First, the higher bandwidths allow larger volumes of data to transmit in a shorter amount of time. This has become increasingly important as the size of data transmissions has continually grown. Modern examples of this desire for broader telecommunications bandwidths include the medical community's desire to a transmit optical images of, for example, x-rays and CAT scans between remote hospitals and physicians. Such transmissions require greater bandwidths to transmit the large size data files in reasonable amounts of time. Another example is the desire for interactive video in homes and offices, for such applications as in-home movies-on-demand and video teleconferencing. The size of the data files to provide home video and real time video are simply too large to be feasibly transmitted without large increases in the available effective transmission throughput.
Conventional approaches to signal transmission on conductive wire lines is to voltage modulate a signal onto the conduit at a frequency that lies within the bounds at which the conduit can electrically conduct the signal. Because of this conventional approach, known modes of conductive wireline transmission are limited in available bandwidth to a spectrum within which the conductive wire line is able to electrically transmit the signal via voltage modulation yielding a current flow. As a result, costly and complicated schemes have been developed to increase the bandwidth and throughput in conventional conductive wireline communications systems using sophisticated switching schemes or signal time-sharing arrangements. Each of these methods is rendered costly and complex in part because the systems adhere to the conventional acceptance that the conductive wire time provides an available bandwidth constrained by its conductive properties.
Several conventional methods have thus been developed to increase bandwidth for the transmission of telecommunications signals over conductive wire lines. These systems illustrative how conventional thinking has constrained the available bandwidth on conductive wire lines, unless expensive and complex systems were added to channel the information onto the conduit more rapidly. Some of these conventional methods are described in Networked Media Sends A Messages, New Media Maps (Nov. 1992) and is ISDN: a snapshot Proceedings of IEEE, Vol. 79 No. 2 (Feb., 1991) and are summarized below.
1. Conventional Method: Plain Oil Telephone Service (POTS)
Bandwidth: 4 Kbps--19.2 Kbps
POTS is offered over copper wires and represents the lowest level on the bandwidth spectrum. It generally records between 4 Kbps and 19.2 Kbps in available bandwidth, but can be upwardly adjusted with fast modem and data compression techniques.
For example, a 14.4 Kbps V.32bis modem coupled with a 4 to 1 signal compression of V.42bis will theoretically provide throughput of more than 50 Kbps. In practice, however, over a typical business line, data can only be moved at about 20 Kbps to 30 Kbps. Even utilizing V-Fast standards that run at 19.2 Kbps, with a total of 112 Kbps theoretically possible after data compression, many analysis believe that without improvements to the copper lines themselves, this is as fast as data transfer is going to get over dial-up copper lines without major infrastructure modifications.
2. Conventional Method: Switch 56
Bandwidth: 56 Kbps
This method requires a special, dedicated copper lines infrastructure and provides a single 56 Kbps channel. An installed base of these signal channel leased copper lines is in operation, and their greater bandwidth makes them a better choice than POTS for fast data transfer, such as for unidirectional video-conferencing. Installing the base of copper lines is, however, expensive. They are also limited to only the single 56 Kbps bandwidth channel and thus do not provide fast enough data transfer to support, for example, simultaneous video data conferencing.
3. Conventional Method: Basic Rate ISDN (B-ISDN)
Bandwidth: 56 Kbps.times.2 bearer+16 Kbps data
Integrated Services Digital Network (ISDN) provides two 56 Kbps voice grade channels and one 16 Kbps data channel. It requires expensive and complex digital switches, which transform all inputs into binary digits. ISDN requires a special structure, so for the ISDN to operate as a universal system for data transfer, approximately 700 million existing global telephone lines must be converted into the ISDN structure. So far, less than 1% of those lines have been converted to support the ISDN and those have been installed mostly in campuses or large company settings.
Standard ISDN, with two 56 Kbps channels and one 16 Kbps channel is sometimes referred to as narrowband ISDN (N-ISDN). Because of the limited bandwidth available in N-ISDN (112 Kbps+16 Kbps), it is inflexible for high resolution graphics, realtime video, medical imaging transmission and other high data volume applications. Available bandwidth under N-ISDN is not sufficient for modern or future requirements.
As a result of the bandwidth limitations of N-ISDN, various schemes have been proposed to increase the bandwidth of ISDN to Mbps levels. These methods are sometimes referred to as broadband ISDN (B-ISDN) and may involve multiplexing multiple channels. Schemes for multiplexing numerous N-ISDN channels, for example, may achieve bandwidths of several Mbps (ex. 29 channels.times.64 Kb/s=1.9 Mbps), but they do so at great cost. They require expensive switches and multiplexers, as well as sophisticated signaling schemes. Other forms (and drawbacks) of B-ISDN, including T1 multiplexing and ATM multiplexing, are discussed more specifically below. But, in general, B-ISDN can be characterized as providing higher data throughputs through the use of special and expensive switches and equipment.
4. Conventional Method: Switches 384 (Fractional T-1)
Bandwidth: 384 Kbps
At 384 Kbps Fractional T-1 provides enough bandwidth for 30 frames per second of low quality video utilizing an advanced version of the X.25 packet switching standard. This requires expensive modifications at both the central office as well as the customer premises.
5. Conventional Method: T-1, Primary Rate ISDN (PRI)
Bandwidth: 1.54 Mbps
T-1 provides a complete digital service, allowing 23 voice grade channels and two data channels. It does so, unfortunately, at great expense. To provide this T-1 capacity to residences for proposed video on demand services, for example, Bell Communications Research is proposing an Asymmetrical Digital Subscriber Line (ADSL) which would use electronic signal processing to raise weak transmissions to acceptable levels of 1.54 megabits per second (Mbps) across 18,000 feet over existing copper. Still in the prototype stage, ADSL, requires interface cards at the central company office and at residences, as well as a television decoder and line conditioning of various forms.
6. Conventional Method: Ethernet and Token Ring
Bandwidth: 10 Mbps & 16 Mbps
Ethernet is the dominant Local Area Network (LAN) architecture with a 10 Mbps rate. The IBM standard Token Ring is more costly and less open and provides up to 16 Mbps. Typically these methods provide adequate access to large digital data files via a small packet burst delivery mode, but suffer from significant performance problems with the delivery requirements of video and audio files, because it was designated to handle sporadic "Bursty" types of information not continuous high volume streams that require synchronization to a time base.
7. Conventional Method: T-3
Bandwidth: 45 Mbps
T-3 is the distribution backbone of the telephone system at 45 Mbps. It can provide broadcast quality NTSC video signals, but is extremely expensive to deploy, due to the number of voice grade lines (about 600) that must be multiplexed and demultiplexed using expensive hardware at both the central and customer facilities.
8. Conventional Method: Fiber Distributed Data Interface (TDDI)
Bandwidth: 100 Mbps
A development by IBM that provides a LAN and WAN technology to delivery 100 Mbps. FDDI has application over optic fibers or copper lines as the conduit. When utilizing fiber optics, FDDI can link up to 500 users at a distance of 500 kilometers. Cost of the fiber installation is extremely high. Copper line FDDI has been reasonably successful in computer local area networks but lack the original capacity of fiber optics that make it useful in broad deployments.
9. Conventional Method: Asynchronous Transfer Mode (ATM)
Bandwidth: 155 Mbps to multiple Gbps over optic fiber
ATM is an outgrowth of ISDN and is designed to integrate multiple data types at varying speeds with dynamic bandwidth allocation. Throughput starts at 155 Mbps, with theoretical limits approaching the Gbps level. ATM technology is extremely costly, requiring significant infrastructure outlay and modification and constant upgrading of the ATM switching software to control data flow and channel allocation.
With the exception of the fiber optic systems, all of the above systems constrain the available bandwidth by adopting the conventional approach to signal transmission, that is, to voltage modulate a signal onto a conduit at a frequency that lies within the bounds of the conduit's ability to support the signal through its conductive properties producing a current flow. As a result, the signals travelling on the conduit must be coordinated with other traffic by expensive switches, processors and protocols.
Bandwidth expansion has also been constrained in the wireless transmission area. There are several wireless modes of communications, chiefly cellular and traditional wireless. Cellular phase technology is currently straining at the boundaries of 19.2 Kb/Second of throughput (utilizing Cellular Digital Packet Data technology). The chief limitations of cellular throughput are a direct result of the Time Division Multiple Access (TDMA) schemes utilized, and the traditional analog approach to spectrum usage. Coupled with the noise and interference that accompanies these transmission modes, the noise floor rapidly overcomes the available power of the transmitter. As a result, the receivers are unable to separate noise from the information transmitted.
As is well known, conductive wireline communications and wireless communications suffer from performance limitations caused by signal interference, ambient noise, and spurious noise. In conventional transmission systems, these limitations effect the available bandwidth, distance, and carrying capacity of a transmission system employing the wireline or wireless communication systems. With both wireless and wireline communication systems, the noise floor and signal interference in the transmission conduit rapidly overcome the signal transmitted. This noise on the wireless or wireline communications conduit is a significant limitation to the ability of conventional systems to expand their available bandwidth.
The conventional wisdom for overcoming this limitation was to boost the power (i.e., increase the voltage of the signal) at the transmitter to boost the voltage level of the signal relative to the noise at the receiver. Without such boosting of the power at the transmitter, the receivers were unable to separate the noise from the desired signal. While some have tried to apply digital means to improve the signal-to-noise ratio while reducing power requirements, the overall performance of the systems is still significantly limited by the accompanying noise that is inherent in the transmission system used.
Qualcomm (U.S. Pat. No. 4,901,307), for example, has applied a digital Code Division Multiple Access system to achieve improvements in signal quality and power utilization, as well as a modest increase in bandwidth compared to TDMA technology, nevertheless, the improvements in bandwidth are relatively small.
Improving the transmission bandwidths across existing telecommunications conduits, without limiting carrying distances or capacities and without having to increase power to overcome noise floors, is desirable.